Antenna masts for high altitude flight must provide adequate shielding of the electrical components against corona discharge during transmissions. Antenna masts which are generally suited for use at altitudes below about 30,000 feet above sea level have been found to be wholly unsuited for use at higher altitudes due to corona discharge from the electrical components at the lower air pressures involved at such higher altitudes. This problem is particularly acute in antenna masts for operation in the high frequency range of from about two to thirty-six megacycles, where it is common to use transmitting powers of the order of five hundred to one thousand watts or higher. The presence of corona is objectionable due to the dis sipation of RF energy and noise, and the shortened life of the components due to the heating and destruction by the corona flame.

A particular requirement of such antenna masts is that they include or be adapted to include a lightning arrester to protect the electrical components carried within the aircraft from damage due to lightning strikes on the sin tenna mast or on the wire connected thereto. However, the provision of a lightning arrester within the mast body further complicates the corona problem, due to the increased area of exposed metallic parts of the arrester. There is also a requirement for antenna masts which are convertible for use either with or without a lightning arrester, which can operate above thirty thousand feet in either mode, and which can be converted readily and quickly.

It is therefore an important object of this invention to provide a high altitude antenna mast which may be used either with or without a lightning arrester.

A further object of this invention is to provide a mast for use at altitudes from sea level to at least 50,000 feet incorporating a lightning arrester including provision for the suppression of corona discharge from exposed internal metallic parts.

Another object of this invention is to provide an antenna mast, as outlined above, particularly adapted for providing electrical connection to a long wire antenna for use in the high-frequency part of the radio spectrum and being convertible from a mast having no lightning arrester to a mast incorporating a lightning arrester.

Another important object of this invention is the provision of an antenna mast including provision for electrically connecting radio equipment with a long-wired antenna and providing a corona suppressing seal at the junction of the fixed mast electrical components and the lead-in component which seal is eifected concurrently with the assembly of the parts.

A still further object of this invention is the provision of an antenna mast for long-wire antennas which incorporates the lightning arrester and provides substantially one atmosphere of pressure for the internal exposed metallic parts of the arrester to suppress corona discharge therefrom when flown at high altitudes.

These and other objects of the invention will be apparent from the following description, the accompanying drawings and the appended claims.

In the drawings:

FTG. 1 is a vertical sectional view, partially in elevation, of an antenna mast constructed according to this invention;

FIG. 2 is a transverse section through the base of the mast, taken generally along the line 22 of FIG. 1;

FIG. 3 is a further transverse section through the mast base taken generally along the line 3-3 of FIG. 1, showing the retainer ring;

FIG. 4 is an enlarged fragmentary section of a portion of FIG. 1 showing the electrical coupling and corona seal between the antenna lead-in wire and the mast electrical terminal;

FIG. 5 is another enlarged fragmentary section showing the lower end of the support tube and the tube supporting nut;

FIG. 6 is a fragmentary vertical section of the lower portion of the mast of FIG. 1 showing a lightning arrester installed therein, and

FIG. 7 is a fragmentary enlarged section of a portion of 6 showing the electrical connection and seal between the lightning arrester and the mast.

Referring to the drawings, which illustrate preferred embodiments of this invention, a mast constructed according to this invention is illustrated generally at 10 as including a body 11 formed of molded plastic dielectric material. Preferably, the body 11 is formed of material which has high resistance to weathering and to rain erosion. The body of the mast is streamlined and extends upwardly to support an antenna wire 12 above the surface of the vehicle to which it is attached. The mast 10 preferably includes a barrel or chuck assembly 13 molded in the upper portion thereof for forming an electrical and mechanical connection with the inner end of the wire 12. The upper portion of the mast, including chuck assembly 13 may be constructed according to the teachings of the patents to McGee 2,626,353 or Matson et al. 2,647,941. Preferably, a molded flexible plastic lead through wire support or bushing 14 is threaded into the body, and provides support for the antenna wire 12 at the head of the mast 10.

The mast 10 is mounted on the aircraft or other such vehicle, through a prepared opening formed in the skin 15 of the aircraft. The body 11 of the mast 10 is preferably circular in section at the base thereof and is proportioned to extend inwardly through the aircraft skin 15 a distance beneath the aircraft skin surface. The support means for the mast 10 includes a generally tubular mast mounting sleeve which forms a circular mounting flange as indicated at 21. The sleeve 20 is assembled over the lower end of the mast body and is bonded thereto with the flange positioned for engagement with the aircraft skin 15 at the prepared opening. The outer surface of the mast adjacent the bottom thereof may be provided with a shallow cylindrical recess indicated at 23, and the inner surface of the sleeve 20 may be provided with threads or grooves 24 through which a suitable binder material may be injected through an opening 25 formed in the sleeve 20. In this manner, the sleeve 20 is bonded to the body 10 to form a rigid mechanical and weathertight seal therewith. Alternately, sleeve 20 may be molded integrally with the mast to accomplish the bonded attachment.

The lower end of the mast 10 is formed with an inwardly or downwardly opening, generally conically shaped cavity 30, which opens through the bottom of the mast body below the aircraft skin reference line in the mounted position of the mast. An electrical mast conductor is molded into :the mast body, and consists of a hollow brass tube 32 connected at its upper end by :a silver braze to the chuck assembly 13. The lower end 33 of the tube 32 terminates at the apex of the cavity forming one-half of a terminal connector portion for the mast. A brass corona sup pression ring 35 is soldered to the lower end 33 and is partially embedded into the body lit. The hollow lower end 33 of the conductor rod 32 forms the female portion of an electrical connector for receiving an operating conhector portion leading to the associated aircraft radio equipment.

The rod 32 may be either hollow, as shown, or solid with an opening or other connector means at the bottom thereof at the cavity 3t). Where the hollow rod 3?. is used, the interior is preferably sealed by a polyethylene 'plug 95'. The tube or rod 32 should have a smoothly polished surface, such as a silver plated surface, to keep RF losses to minimum.

FIG. 1 shows the mast assembled in position on an aircraft wherein the mast is used without a lightning arrester. The mast body is held in place on the skin by a retainer ring as having a plurality of fastener devices, such as fixed nuts 41. The ring it) is positioned on the inside surface of the skin beneath the flange 21 for fastening by screws 42..

Subsequent to installation an outer tubular mounting sleeve 45 is positioned in telescoping relation over the sleeve 20. The outer sleeve 45 includes an outwardly extending radial mounting fiange 46 at the bottom thereof, and the tubular portion thereof is vertically slotted at 47 (FIG. 2) to permit it to be clamped onto the sleeve An external clamp formed in two clamping halves t) and 51 with clamping flanges 52 thereon may be assertbled over the outer sleeve 45 and tightened at the flange 52 by bolts 53. The external clamp secures the outer sleeve 45 tightly about the inner sleeve and with the flange 46 thereof extending just below the bottom edge of the mast body at the opening 30. This clamp also provides means for connecting a support or brace to the bottom of the mast.

Closure means for the cavity includes a bottom closure plate formed with a peripheral depression or recess di and proportioned for attachment to the mast at the radial flange 46 by a plurality of attaching bolts 63. The plate 60 is provided with a central threaded through which a plastic, dielectric lead-in wire support tube may be readily inserted from the bottom. Prior to the insertion, the tube 7 it is assembled over the end of a prepared antenna lead-in cable or wire 72. The lead-in Wire '72 supports a male plug or coupling '75 soldered on the exposed end of the conductor wire 76. The end of the Wire 72 is preferably sealed by a band 77 of heat shrunk, high dielectric thermoplastic material. As shown in FIGS. 1 and 4, a short portion of the wire 72 protrudes above the support tube 70.

Means for forming a corona and air seal at the connection of the plug and the mast at the rod 32 includes an elastomeric sealing sleeve Sill, preferably formed of high dielectric material such as silicone rubber, which is assembled over the exposed end of the lead-in wire 72 against the upper end of the tube 7%. The body of the mast is provided with a suitable cylindrical recess 82 at the apex of the cavity 39 in surrounding relation to the rods lower connecting end 33, for receiving at least the upper part of the sealing sleeve 89. The outside diameter of the sleeve 39 conforms generally to the diameter of the tube "ill at the upper end thereof to form a tight air-eliminating and corona suppressing fit within the recess 82. Preferably, a pair of Teflon, polyethylene, or other suitable washers 83 are interposed between the tube 7b and the sleeve to form .a bearing surface providing for the rotation of the tube 70 in tightening without damaging the sleeve 80. The taper of the cavity at 39 leads to the body recess 82 and facilitates the assembly of the parts.

Means for compressing the sleeve 80 to the recess 32 tightly about the exposed end portion of the lead-in '72 while supporting the lead-in cable, includes the tube 79 which has a tapered lower end as indicated at 85, in PEG. 5. The tube end 35 is provided with a plurality of vertically extending slots 36 terminating in strain relieving opening a openings 37. A nut 99 is provided with a suitably tapered internal opening t ll and is adapted for threading into the bottom plate opening 65. The assembled position of the parts are shown in enlarged detail in FIG. 5, where it can be seen that the slots 36 permit the bottom end of the tube Til to be clamped tightly about the lead-in wire 72. The taper at 85 is such as first to cause the tube to move upwardly to compress the sleeve till upon the initial tightening of the nut 5'9 to form the seal. Upon further tightening of the nut hit, the resistance of the sleeve prevents further movement of the tube 76 and the lower end of the tube 70 is clamped by the nut 94? about the wire '72, thus locking the wire secure to the mast. Preferably, the not 9@ need only be tightened finger tight to effect both the upward movement of the tube 70 to compress the seal formed by the sleeve 89 and to effect the clamping of the tube 7% on the wire 72 by the collet action of the nut. The high voltage seal provided by the sleeve 80 eliminates all air and the possibility of corona forming at the connection.

The arrangement of the parts of the mast of this invention is particularly adapted for the incorporation of a lightning arrester, with a minimum of time and without modification to the mast body. The mast is constructed so that the steps necessary to incorporate a lightning arrester therein can be readily accomplished, either on a bench or with the mast installed in the aircraft. These steps include the removal of the tube 76 and the lead-in wire 72 together with the plate 69, and insertion of the arrester. The arrester then becomes the electrical feed through member of the mast connecting the internal mast electrical components with the external antenna conductors.

Referring to FIG. 6, a lightning arrester is installed Within the mast lit. The lightning arrcster 1% may be constructed according to the teachings of United States Patent Nos. 2,906,922 and 2,906,925, and includes a metal cylindrical body ldl terminating in an annular mounting flange M2. The arrester 100 includes a lower glass bushing 1% supporting an antenna terminal post 106 and a metal corona ring ill? on the lower end thereof.

The lead-in wire 72 is now connected directly to the arrester 1% by means of a molded plastic antenna connecting terminal assembly 108 which is mounted on the post 1&6. The assembly 108 preferably includes a female metallic socket member 199 for receiving the plug or end terminal '75 of the wire 72. The plastic body of the assembly is recessed to receive an elastomeric high voltage sealing sleeve llltl similar to the seal Ell, which is held in compressed relation about the end of the wire 72 by a connector not 1112.

A glass bushing is formed on the upper end of the arrester still. The bushing 115 is proportioned to be received substantially wholly within the cavity 39, and terminates in an upper metal ring 116 supporting a terminal binding post 12%.

The arrester lot? is connected to the mast terminal at the rod 32 by means of a metal stem 121 having a lower end threaded onto the post 126. The upper end of the stem 121 supports a male plug 125, similar in configuration to the plug '75. The length of the stem 121 is such that the plug 125 is received in the rod 32 when the upper glass bushing 115 is received within the cavity 3% The stem 121 is shouldered at 129 to support a plastic tube 13% mounted over the stern 121. The tube 13A) is preferably formed of the same material as the tube '70 of FIGS. 1 and 4, and has the same configuration as the upper portion of the tube 7%. An upper portion of the stem 121 and plug 125 extend beyond the tube 130, as shown in FIG. 7. The high voltage silicone rubber sleeve 8% and the high voltage washers 83 may then be assembled on the tube 13th over the exposed upper end of the stem 121 in the same manner that they were as sembled on the upper end of the tube 70 over the upper protruding end of the lead-in wire 72.

The embodiment of the invention shown in FIG. 6 includes means for forming an air-tight seal both at the sealing ring 80 and at the junction of the arrester 100 with the mast body 11, in order to provide a controlled pressure within the cavity 30 surrounding the exposed metallic parts 116 and 121. Preferably, the invention includes means for assuring that the pressure within the cavity 30, with the lightning arrester installed, remains substantially at the same pressure which was present at the time of installation, which usually corresponds substantially to one atmosphere of pressure. The maintenance of an atmosphere of pressure within the chamber 30 at the exposed metal parts of the lightning arrester assures that the potential required for corona discharge remains well above that at which corona occurs in use.

Means for sealing the cavity 30 at the junction of the arrester flange 102 and the mast includes a sealing spacer disk 140 which is recessed at 141 to receive a silicone rubber sealing ring 145 between the disk 140 and the bottom surface of the mast body 10. When the disk 140 is drawn tightly up against the flange 46 of the sleeve 45, the ring 145 is compressed to form an airtight seal. A sealing gasket 148 is also placed between the flange 102 and the disk 140 to provide an effective air-tight seal between the arrester body and the disk 140. The dimensions of the tube 130 in relation to the shoulder on the stem 121 is such that the tightening of the arrester 100 to the mast by the bolts 150 serves to compress the silicone rubber high voltage seal 80 within the recess 82, thereby assuring that an eifective, air-tight seal is maintained at the electrical connection of the arrester with the rod 32 within the mast body, while, at the same time, effecting an air-tight seal between the arrester body 101 and the mast body 11.

It will therefore be seen that this invention provides a mast characterized by versatility and by an ability to operate at high altitudes. In one embodiment, it incorporates a lightning arrester providing controlled environmental conditions for the exposed, corona producing parts of the arrester. The arrester may be removed and the lead-in wire applied directly to the electrical connection within the mast body using only tools which are readily available in the field, and without the necessity of removing the mast from an aircraft on which it may be installed. In either mode of operation, whether the mast is being used with or Without a lightning arrester, the arrangement of the parts assures that an effective high voltage, corona eliminating seal is effected by the assembly of the parts.

While the forms of apparatus herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise forms of apparatus, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. A high altitude antenna mast for supporting a long wire antenna and providing an electrical connection thereto, comprising an insulating supporting body adapted for mounting in extending relation from the surface of an aircraft and having means'in the outer end thereof forming an electrical connection with an antenna wire, means in said body defining a cavity, an electrical conductor in said body extending from said antenna wire connecting means and terminating at a terminal connector portion at said cavity, an electrical feed-through member removably received in said cavity and having a cooperating terminal connector on an inner end thereof electrically engageable with said connector portion, elastomeric seal means between said feed-through member and said body in surrounding relation to said feed-through member adjacent said inner end thereof and supported in air-sealing relation to said connector by said feedthrough member, and feedhrough member retaining means joining said body at said cavity securing said member in engagement with said seal means holding said seal means in axial compression in said air-sealing relation protecting said electrical connection from exposure to low pressure air at high altitudes.

2. The antenna mast of claim 1 wherein said feed through member comprises a dielectric hollow tube, and an antenna lead-in wire in said tube with said cooperating terminal connector formed on an inner end and having extended outer end, and said feed through member retaining means including a bottom plate connectable to said body at said opening, and a hollow nut threaded into said plate engageable with said outer end of said tube to effect inward movement of said tube into said body against said elastomeric seal means.

3. The antenna mast of claim 1 wherein said feedthrough member comprises a lightning arrester having an inner end received in said cavity and with said cooperating terminal connector carried on said inner end and engageable with said terminal connector member of said body, further sealing means between said arrester and said body forming an air-tight seal with said body and said cavity, and arrester retaining means connecting said feed through member to said body at said further sealing means for isolating said cavity substantially at atmospheric pressure with said arrester installed therein.

4. An antenna mast comprising, a dielectric wire supporting body adapted for mounting on an airframe with a portion thereof extending inwardly of the airframe skin reference line, means in said mast defining a cavity opening below said reference line, an electrical mast connector in said body at said cavity, means in said body defining a seal receiving recess in surrounding relation to said connector at said cavity, an electrical lead-in component received in said cavity having an electrical fitting on an end thereof proportioned to engage said connector and having a dielectric tube proportioned to form a clearance fit with and extending partially into said recess, an elastic high voltage seal in said recess between said body and said tube in surrounding relation to said lead-in component, and means securing said lead-in component to said body closing said cavity with said tube compressing said seal within said recess tightly about said electrical fitting at said connector to suppress corona at the electrical junc tion formed thereby.

5. A high altitude antenna mast for supporting a long wire antenna and providing an electrical connection thereto, comprising an insulating supporting body adapted for mounting in extending relation from the surface of an aircraft and having means in the outer end thereof forming an electrical connection with an antenna wire, means in said body defining an inwardly opening cavity, an electrical conductor in said body extending from said antenna wire connecting means and terminating at a terminal connector portion at said cavity, an essentially rigid support support tube in said cavity, a lead-in wire received in said tube and having a cooperating terminal connector on an inner end thereof electrically engageable with said connector portion, an elastomeric sealing sleeve mounted on an end of said tube in surrounding relation to said lead-in wire, means in said body defining a recess receiving said sleeve at said connector member, and tube retaining means securing said tube with said sleeve axially compressed in air-sealing relation about said wire in said recess protecting said electrical connection from exposure to low pressure air at high altitudes.

6. A high altitude antenna mast for supporting a long wire antenna and providing an electrical connection thereto, comprising an insulating supporting body adapted for mounting in extending relation from the surface of an aircraft and having means in the outer end thereof forming an electrical'connection with an antenna wire, means in said body defining a cavity, an electrical conductor in said body extending from said antenna wire connecting means and terminating at a terminal connector member at said cavity, a lightning arrester rernovably received in said cavity and having a cooperating terminal connector on an inner end thereof electrically engageable with said Connector member, elastomeric seal means between said arrester and said body formed in surrounding air-sealing relation to said connector, and arrester retaining and sealing means joining said arrester to said body at said cavity securing said arrester within said cavity and compressing said seal means in air-sealing relation at said electrical connection and also forming an air-tight seal with said cavity for holding said cavity isolated from exposure to low pressure air at high altitudes.

7. A high altitude antenna mast for supporting a long wire antenna and providing an electrical connection thereto, comprising an insulating antenna wire supporting body adapted for mounting in extending relation from the surface of an aircraft and having means in the outer end thereof for gripping and forming an electrical connection with an antenna wire, means in said body defining a cavity,

an electrical conductor in said body extending from said Wire junction and ending at said cavity forming a terminal connector portion at said cavity, an electrical feed-through member including a dielectric tube removably received in said cavity and having a cooperating terminal connector extending from an end of said tube electrically engageable with said connector portion, an elastomeric sealing sleeve mounted on said tube in air-sealing relation to said connector, means in said body defining a recess at said terminal connector proportioned to receive said sleeve, and feed-through member retaining means joining said body at said cavity securing said member with said sealing sleeve axially compressed in air-sealing relation in said recess about said connector protecting the electrical connection with said mast body from exposure to low pressure air at high altitudes.

8. A high altitude antenna mast for supporting a long wire antenna and providing an electrical connection thereto, comprising an insulating antenna wire supporting. body adapted for mounting in extending relation from the surface of an aircraft and having means in the outer end thereof for forming an electrical connection with an antenna wire, means in said body defining a cavity, an electrical conductor in said body extending from said wire junction and ending at said cavity forming a terminal connector portion at said cavity, an electrical feed-through member including an essentially rigid dielectric tube removably received in said cavity end extending exteriorly of said cavity and forming a tapered wire-gripping portion at the extended end thereof, a lead-in Wire in said tube and having a cooperating terminal connector extending from the upper end of said tube thereof electrically engageable with said connector portion, an elastomeric sealing sleeve on the inner end of said tube in air-sealing relation to said connector, a feed-through member retain ing plate closing said body at said cavity, and a nut threaded in said plate engaging said tube at said wire gripping portion and operable when tightened to move said tube against said sealing sleeve to compress said sleeve into air-sealing relation about said connector, and further operable to clamp said tube about said lead-in wire with further tightening of said nut.